Means for interconverting alternating and direct currents.



J. L. WOODBRIDGE Mms ron mmcowvzmme mumums AND DIRECT CURRENTS.

APPLICATION FILED JULY 16. I915- N 1,244,569, 7 Patented Oct. 30, 191.

2 SHEETS-SHEET I.

l i i l'm lll l IIIVEN TOR WI TIMES I TTOBIIEV.

J. L. WOODBRIDGE.

MEANS FOR INTERCONVERTING ALTERNATlNG-AND DIRECT CURRENTS.

APPLICATION HLED JULY 16. I915.

Patented Oct. 30, 1917.

2 SHEETS-SHEET 2.

INYENTDR v/dsgdfi lesfer 145M522" e W (as ITTDRHEY.

; nivrra JOSEPH LESTER WOODBRIDGE, 0F PHILADELPHIA, PENNSYLVANIA.

MEANS FOR INTEBCONVERTING ALTERNATING AND DIRECT CURRENTS.

Application filed July 16, 1915.

To all whom it may concern Be it known that I, JOSEPH Lns'rnnVVoonnnrnsn, a citizenof the United States, and a resident of the cityof Philadelphia, in the State of Pennsylvania, have invented certain newand useful Improvements in Means for Interconverting Alternating andDirect Currents, of which the following is a specification.

My invention relates to apparatus for converting alternating currentinto direct current, or vice versa, and especially to such convertingapparatus in which there is a magnetic structure, all parts of which arerelatively fixed, upon which are wound suitable coils or windingsconnected to the AC and DC circuits; such apparatus, for example, asdescribed in my Patent No. 880,705.

The object of my invention is to provide more eflicient and lessexpensive means for effecting the interconversion of alternating anddirect currents, to improve the commu tation in apparatus designed forthis purpose, and further to provide improved means for rotating suchconverting apparatus.

These and other objects of the invention -will be more clearlyunderstood by reference to the following description in connection withthe accompanying drawings, in which, I Figure l is a diagrammatic viewof apparatus involving features of the invention, and arranged forconverting 2 phase alternating currents into direct current or viceversa.

Fig. 2 illustrates details of one section of the winding shown in Fig.1.

Fig. 3 is a diagrammatic view of apparatus similar to that shown in Fig.1, except that it is designed for connection to a 6 phase circuit, and aspecial split pole converter is used for driving, and

Fig. 1 shows an alternative method of connecting the alternating currentcircuit to the windings of Fig. 3.

Referring to Fig. 1, 1 is a magnetic structure similar to the iron coreof a dynamo armature, preferably made up of laminations of iron, andprovided with 4 openings, 2, 3, 4E, and 5 near the periphery, throughwhich openings pass the conductors of the windings 6, 7, 8 and 9. Thewinding is Specification of Letters Patent.

Patented Oct. 30, 1917.

Serial No. 40,190.

thus divided into four sections, all of the turns of each sectionpassing through the corresponding opening in the iron core so that allof the turns in any one section embrace the same portion of the magneticcircuit. The object of this construction is to insure that any magneticflux that passes through one turn of the winding shall pass through allthe other turns in the same section, In order to secure this result moreeffectively and prevent leakage of flux between adjacent turns of thewinding the conductors are preferably made of flat strip, as shown morein detail in Fig. 2, which shows the conductors of sections 6 of thewinding to an enlarged scale and partly in section. This constructionincreases the reluctance of the leakage path for magnetic lines betweenadjacent conductors by increasing the length and reducing the crosssectional area of such paths.

The object of this construction will be explained later.

Referring to Fig. 1 a commutator 10 is shown connected in the usualmanner to the windings 6, 7, 8 and 9. Upon this commutator rear fourbrushes, 11, 12, 13 and 14, of which one pair, 13, 14 is short-circuitedby conductor 26, while the other pair, 11, 12, is connected'to thedirect current circuit 15, 16. The magnetic structure 1 with itscommutator and windings is mounted on a shaft 17, which may be driven bya suitable direct current motor M connected across the circuit 15, 16.A. suitable source of direct current, such as the battery B may beconnected across the circuit 15, 16. On the shaft 17 are also mountedcollector rings 18, 19, 20 and 21 connected to points in the windingintermediate between the sections 6, 7, S and 9. Suitable brushesbearing upon the collector rings are connected to the two phasealternating current circuit 22, 23, 24, 25. To the latter circuit asource of two phase alternating current A is connected, as well astranslating devices L. A two phase synchronous motor M is also shownmechanically connected to the shaft 17 and electrically connected to thetwo phase circuit 22, 23, 2 1, 25. Suitable switches are shown forconnecting or disconnecting the motors M and M to the corresponding cir-;ringslS, :19, 20, 21, and alternating currents may,itherefore,s.betaken from these collector rings fforthe translating-devices L, or-thealternating currentv source A, .if operating .Assuming firstthat thesource of alternating currentaA iszdisconnected and'the magneticstructure 1 with its windingsandcommutator is being rotated by meansofthe motor M, a. small amount. of. direct current passing pfronrthecircuit 15, 16 through the windings 56,11,18, Qlby way .of the brushes11 andf12 willproduce a primaryicomponent.of mag- .netic flux inthescwindings in the direction of the arrows K K :K and 'K. Intheposition showninthc drawing, currenttfrom 25:

two parts, one partpassing through sections 6 and 7, and the otherthrough sections 9 and .-8 to brush '12. .As the rotation progresses-inthedirection of the arrow X,'the

conductor '15 entering brush '11 dividesinto current in someofthe coilsof sections 7 5311(1 8 is reversed, thus reducing and finally-revers1ng=the magneticfluxin these two secations. Thischangeof'magnetic fluxinduces an electro-motive-force in the coils affected;thereby, and .this electroTmotive-force .de-

velops a difference of potential between .brushes 13 and 14. Since thesetwo brushes :are short-circuited-by conductor 26, a small flow ofcurrent will take place between these brushes. This currentpassingthrough the .windin'gsb, 7,'8,'9 produces a secondary componentof magnetic flux -represented by the arrows K K K and K The rota-:tionof the converter causes a similar varia- .tion and-reversal-of thissecondarycompo- .nent of'magnetic flux in the. sections of the-.windings, resulting in an .electro-motiveforce between brushes '11 and*12,'which will be counterto-that of the circuit -15, 16. If .theapparatus is properly designed and operated ,at'a suitable speed thiscounterelectrosmotive-iforce will be nearly. equal .to

'athat'of-the circuit 15, 16,.but just enough :less to permitthe.smallfiow: of current into the brushes 11, 12, necessary to establishtheprimaryanagnetio flux described above.

The counter-elcctro-motive-force developedacross the-brushes 11, 12, asdescribed above, will also appear as an alternating currentelectro+motive-force at the collector at; a suitable voltage. andfrequency may be magnetic :flux above described. efiect, therefore, .ofany such alternating connected to the alternating current circuit 22,23, 24, 25. Obviously the rotatlon of the converter .1 must be maintaned in synchro- .nism with the source A, and .to insure this thesynchronous motor M should be used for driving the converter wheneverthe source A is connected. Under these conditions the direct currentmotor M should preferably be disconnected. When alternating currents aretaken from the collector rings '18, '19, 20, 21 in phase with thealternating.electro motive-force across these collector rings, thesecurrents in the windings (3, 7, 8, 9 will, in generalbe opposed to thesmall direct current input at :the brushes '11, 12 necessary to maintainthe primary The first current output .from the converter will beatendency to reduce the counter-electro-motivezforce developed 111 ltsw1ndmgs,.and this reduction will permit an in-put of .direct site to:the alternating currents taken rom thecollector rings. Similarlyif thevoltage .OfftllG source A is raised sufliciently, alternating currentswill be supplied 1 to the concurrent atithe brushes '11, 12 equal and opovcrterincreasing the counter-clectro motiveforceiatthebrushes 11 and:12 until'this exceeds'the .voltage.-of:the battery B and energy willbetransferred from the. source A to the battery. The apparatus, therefore,

.acts as a true :inductive comerter rbetween he' alternating and thedlrect current circuits.

'lVhen thedirect current brushes are in the position shown inthediagram, direct currententeringthe'brush 11 may pass-directly tocollector ring'lS by way of-tap 27 without passing around the magneticcir- .cnit.of;the converter. lVhen,however, the

rotationhas.proceededuntil thebrush 11 is 111 contact with oneof thecommutator bars connected .to an intermediate pointof sectionsGof thewinding,.the current entering -brush 11 .will divide, apartofit passingto .the tap.27.and the balancegoing to tap 28.

This division of current will be such as to reduce 'thetotal-ampereturns in section 6 practically to. zero, except for the smallexciting'currcntsnecessary to maintain the counter-electro anotive forceas described above. Forexample,.if'brush llis in contact .with the nextcommutator bar to that shown so that. there will be one turn betweenrbrush illand tap 27, and5 turns between ibrush 11.and tap 2S,thenonesixth of the total current entering brush 11 with pass to tap 28,andifive-sixths.totap127, thus the one-sixth of :the current passingthrough fivezturns ofsection 6 willjust balanceithe 'fiye1sixths ofithecurrent passingin the opposite: direction'through. one turn. Thisdivision of current at any. point in the rotation will: be: broughtabout owing tothe fact that there are direct current brushes.

any small departure from it will produce brush. In other Words, theremust be the same'num'ber of alternating current taps as struction verymaterially reduces the tendency to sparking at the brushes, and alsoavoids the tendency to magnetic saturation in sections of the magneticcircuit.

The short-circuit conductor 26 in addition to providing a path for theexciting current necessary to develop thecounter-electro-motive-forcerequired across the brushes 11, 12 has also another important function.If the alternating current on the two phases of the circuit isunbalanced, for example, if all of the load is taken from the twoconductors 22, 24,0r if the load on these two is greater than that takenfrom the conductors 23, 25, a part of this excess current will passthrough conductor 26 in certain positions of the brushes'on thecommutator. This result also occurs if the converter is used fortransforming single phase alternating current into direct current.

In F 1g. 3 a modificatlon of the invention is shown in which theconverter is adapted for connection to a 6 phase alternating currentcircuit. The magnetic core 51 is provided with six openings 52, 58, 54,55, 56 and 57 on which 'are wound, respectively, the groups of coils 58to 63. These coils are connected to the commutator 6a in the usualmanner, but in order to avoid confusion most of the conductorsconnecting the coils to the commutator bars have been interrupted on thedrawing. SiX brushes are shown bearing on the commutator numbered from65 to 7 O, inclusive. Brushes 65 and 69 are short circuited as well asbrushes 66 and 68. Brushes 6a and 67 are connected to the oppositeterminals of a storagebattery B and brushes 70 and 68 are connected tothe opposite terminals of a second storage battery B Under usualconditions of operation the positive terminal of the battery B will havea different potential from the corresponding terminal of the battery 13There will, however, be certain points in the two batteries which willhave the same potential and may be connected together as. by the switchS. This intermediate circuit between the two batteries will under someconditions of unbalanced AC load, and some positions of the brushes onthe commutator carry a part of the unbalanced current. Under otherconditions this circuit will carry no current This con-' and the switchS need not be closed. The converter 51 is mounted on a shaft 88 whichcarries 6 collector rings numbered from 71 to 76, inclusive, which areconnected to corresponding taps between the adjacent sections of theconverter winding, as shown. These collector rings by means of suitablebrushes are connected to the six conductors of the (3 phase circuit,numbered from 78 to 83, inclusive. To this 6 phase circuit is connecteda source of 6 phase alternating current A and translating devices L.

The shaft 88 is driven by a split pole converter Q, constructed in theusual manner with a bi-polar wound armature 90 provided with the usualcommutator, and six collector rings. The latter are connected to the 6phase circuit, while the commutator through suitable brushes isconnected to the tcrmi nals of the battery B Double throw switches 91and 92 permit the direct current terminals of the converter Q to bedisconnected from the battery B and connected to the battery 13 ifdesired. The converter Q, is provided with main poles 93 and 94s andregulating poles 95 and 96. These latter have their usual function ofvarying the direct current electro-motive-force developed in thearmature without changing the value of the alternating currentelectromotive-force in any marked degree when their excitation isvaried.

The converter Q, is designed to act as a motor for driving the converter51, either from the AC circuit or the DC circuit. It is, however, sodesigned as to prevent any considerable transfer of energy between thesetwo circuits, such transfer being accomplished through the converter 51.This result is secured by a special winding on the regulating poles 95and 96.

The main poles 93 and 9% are provided with an ordinary shunt fieldwinding connected across the brushes of the machine so that theexcitation of the main poles is substantially constant. The regulatingpoles 95 and 96 are provided with a series winding 97, 98 connectedbetween one brush of the machine and the direct current circuit. Thisseries winding is wound in the direction to increase the direct currentvoltage of the machine with any increase of direct current input to theDC brushes. If, therefore, there should occur any tendency to transferenergy between the AC and the DC circuits through the machine Q, achange in the direct current input or output of this machine will varythe counter-electro motive force developed in the machine in thedirection to counteract such tendency.

Furthermore, the regulating poles 95 and 96 are located on thetrailingside of the main poles. This produces a shift of the alternating currentelectro-motive-force of the machine with any change in the excita- Cjition of these regulating poles in the direction to further'counteractthe transfer of energy between the AC and DC circuits. Thus if there isa small .increase of direct current input to the machine Q the strengthof the regulating poles is increased, thus shifting the mean position ofthe total field flux in the direction of armature rotation. This shiftwill retard the phase of the alternating current electro-motive-force developed in the armature of the machine Q causing it to take additionalenergy from the AC circuit in accordance with the usual law ofsynchronous machines of this type. This input of energy from the ACcircuit will oppose any further increase of input from the DC circuit.The shunt field excitation of the machine Q may be adjusted by means ofthe rheostat B, so that when running at synchronous speed the energyrequired to drive the apparatus will be taken substantially all from theDC circuit. Any slight variation in the energy required will be suppliedfrom the AC circuit on account of the action of the regulating poles asabove described. It the supply of alternating current energy from thesource A is interrupted, the machine Q will still continue to drive theconverter 51 and energy will be supplied to the translating devices Lthrough this converter from the batteries B and B \Vhile Figs. 1 and 3show the AC taps taken from points intermediate between the varioussections of the converter winding, this arrangement is not necessary,and these taps may betaken from intermediatepoints in each windingsection instead of from points between'adjacent sections, as shown inFig. 4:. In suchcase it is preferable to take these taps from the middlepoint of each section, in order to secure a symmetrical wave shape ofalternating electro-motive-force. One of the advantages of theconstruction shown in Figs. 1 and 3, and especially thatshown in Fig.3lies in the fact that when current is being transmitted between the ACand the DC circuit, the average current value in the windings of theconverter 51 is comparatively small. It will be noted that there are(ipoints in each revolution of the converter, at which the currentpasses directly from the AC to the DC circuit or vice versa withoutpassing through the converter winding at all.

In other positionsthe current is divided in inverse ratio to the numberof coils through which it is transmitted, so that the heaviest currentis transmitted through the fewest number of coils. This reduces thetotal amount of heating in the winding and permits a smallmachine tocarry comparatively large loads.

Itwill be notedthat in some positions of ,thebrushes, direct currentflows inopposite directions to ,or from an intermediate point in each ofthe Winding sections, the ampere turns on each Side of this intermediatepoint beingequal and opposite. In order to reduce to a minimum theleakage of magnetic flux across the openings 2, 3, 4, 5 under theseconditions, the leakage path should be as long and of as small crosssection as possible. This result is accomplished by making theconductors of thin strips as shown in Fig. 2.

Having described my invention what I claim and desire to secure byLetters Patent is 1. In apparatus of the type described forinterconverting alternating and direct currents, the combination of aplurality of closed magnetic circuits, a group of conducting coilsembracing each of said circuits, said groups connected in series to forma continuous closed circuit Winding, a commutator connected to saidWinding, brushes bearing upon and spaced apart around said commutator atcontact points equal in number to the number of coil groups, shortcircuiting connections interconnecting some of said brushes, alternatingcurrent taps to said winding, one for each coil group, and means forproducing relative rotation of commutator and brushes.

2. In apparatus of the type described for interconverting alternatingand direct currents, the combination of winding sections, a closedmagnetic circuit and an alternating current tap for each section, acommutator connected to the sections and direct current brushes equal innumber to the taps and equally spaced around the commutator.

3. In apparatus of the type described for interconverting alternatingand direct currents, the combination of winding sections, a closedmagnetic circuit and an alternating current tap for each section, acommutator connected to the sections, direct current brushes equal innumber to the taps and immovable in respect to each other, and means forshort circuiting some of said brushes.

4. In apparatus for inter-converting alternating and direct currents,the combination ofa converter devoid of motor function and a motordevoid of converter function for driving the converter, said motordrivable from both the alternating and direct current sourcesimultaneously.

5. In apparatus of the type described the combination of groups ofcoils, closed magnetic circuits one of which passes through all thecoils of each of the respective groups, a commutator connected to thecoils, and alternating current taps and direct current brushes equal innumber to the number of groups and symmetrically spaced.

6. In apparatus of the type described the combination of six windingsections, a closed taps to a six phase alternating current cir 10magnetic circuit and an alternating current cuit.

tap for each section, a commutator 0011- In testimony whereof I haveduly exenected to the sections, six direct current cuted these presentsthis 18th day of July,

: brushes whereo1 two pair are short-cir- 1 915.

cuited, two sources of direct current each JOSEPH LESTER WOODBRIDGE. ofwhich is connected between one of the WVitnesses:

pairs of short circuited brushes and one of J. L. MACBURNEY,

the single brushes, and connections from the WV. G. ROGERS.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. C.

